Piezoelectric materials exhibit a phenomenon known as the piezoelectric effect. This effect can be manifested as a change in electrical properties as a result of applied stress or a stress resulting from an applied electric field. Most piezoelectric materials are crystalline in nature.
Crystalline piezoelectric materials can be described as “electrically stiff” in that relatively large amounts of electric field energy are required to change interatomic distances in the material by a relatively small percentage. As an example, maximum deflection for crystalline piezoelectric materials tends to be around 0.5% in a strong field. An example of a relatively strong field might be one of over 100 V/m.